Instruments which automatically control the engine throttle and supply an indication for control thereof are well known. For example, one of my earlier patents, U.S. Pat. No. 3,486,722 discloses a system wherein the control of the throttle is a function of the combination of two signals. One signal is that of acceleration independent of pitch attitude of the airplane and the other signal is the higher of two alternative signals. The first alternative signal being the airspeed of the aircraft and the second alternative signal being the lift of the aircraft. Both the first and the second alternative signals are deviation signals representing the difference in the first instance between the actual airspeed and a pilot pre-selected airspeed or reference speed and of the second incidence between the actual lift and a pilot un-alterable pre-selected lift that takes flap position into account. The selection between the two alternative signals is performed automatically and not under a pilot's control.
A more recent patent of Lambregts et al. U.S. Pat. No. 5,079,711 discloses an aircraft high altitude vertical flight path and speed control system. As disclosed therein, a variable bandwidth factor KALT is applied in a total energy control system to obtain a reduction in throttle activity while maintaining system stability. The system has a total energy load control loop and an energy distribution control loop. In the former, a net thrust command signal Tc is generated to reduce the total energy error to zero. In the latter, an elevator position command signal Sec is generated to reduce the energy rate distribution error, i.e. correct the distribution of energy between kinetic energy (speed) and potential energy (altitude). The error signal input into each loop has a flight path component and a speed component. The factor KALT is applied to both components of the total energy error to reduce the bandwidth of the total energy error loop with increasing altitude and thereby reduce throttle activity. The factor KALT is also applied to one of the components of the energy distribution error to prioritize reduction of that component to zero by control of the elevator position. Preferably, speed control is prioritized, and energy errors are channeled into short term deviations in altitude.
The prior art systems are effective under many circumstances but have not been found to be effective in compensating for mountain waves. Mountain waves or orographic waves occur frequently over mountain areas, as for example, along the East coast of the United States as a result of strong westerly wind flow conditions. Further, under suitable conditions mountain waves have an influence up through the atmosphere. A problem in using auto throttle systems when encountering mountain waves is that they tend to hunt and peck and result in frequent increases and decreases in throttle to provide a rough or choppy ride for the passengers.
It is now believed that an auto throttle system in accordance with the present invention will anticipate changes in throttle and smooth out the flight. Advantageously such systems may be incorporated in conventional automatic throttle control systems without adversely affecting the operation of such systems. The automatic throttle control systems with mountain wave compensation, also utilize the same inputs and outputs as conventional systems and can be added to systems at a relatively small cost. Such systems are reliable, durable and easily serviced and may be incorporated as a computer program.